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blood and the blood pH. • Bony fish remove the amine portions of amino acids and excrete them as ammonia across the gills. • Elasmobranchs, adult amphibians, and mammals produce and excrete urea, which is quite soluble but much less toxic than ammonia. • Insects, reptiles, and birds produce uric acid from the amino gr...
female reproductive systems are specialized for different functions. Structure and Function of the Male Reproductive System. The testes produce sperm and secrete the male sex hormone, testosterone. Structure and Function of the Female Reproductive System. An egg cell within an ovarian follicle develops and is released...
of two sex cells, or gametes, a term that includes sperm and eggs (or ova). The union of sperm and egg cells produces a fertilized egg, or zygote, that develops by mitotic division into a new multicellular organism. The zygote and the cells it forms by mitosis are diploid; they contain both members of each homologous ...
that these lizards could lay eggs that were viable even if they were not fertilized. In other words, they were capable of asexual reproduction in the absence of sperm, a type of parthenogenesis. Further work has shown that parthenogenesis also occurs among populations of other lizard genera. Another variation in repro...
will give rise to ova or sperm migrate from the yolk sac to the embryonic gonads, which have the potential to become either ovaries in females or testes in males. For this reason, the embry- onic gonads are said to be “indifferent.” If the embryo is a male, it will have a Y chromosome with a gene whose product convert...
the ocean that organisms can use as signals for synchronizing reproduction, but one all-pervasive signal is the cycle of the moon. Once each month, the moon approaches closer to the earth than usual, and when it does, its increased gravitational attraction causes somewhat higher tides. Many marine organisms sense the ...
development within the body of the mother and are then released as small but competent adults. Here a lemon shark has just given birth to a young shark, which is still attached by the umbilical cord. 1198 Part XIV Regulating the Animal Body Fish and Amphibians Most fish and amphibians, unlike other vertebrates, reprod...
some tadpoles, which are the larvae of frogs and toads, grow in a matter of weeks from creatures no bigger than the tip of a pencil into individuals as big as a goldfish. When the larva has grown to a sufficient size, it undergoes a developmental transition, or metamorphosis, into the terrestrial adult form. The eggs ...
the egg passes along the oviduct, glands secrete albumin proteins (the egg white) and the hard, calcareous shell that distinguishes bird eggs from reptilian eggs. While modern reptiles are poikilotherms (animals whose body temperature varies with the temperature of their environment), birds are homeotherms (animals th...
release of a mature ovum from the ovary in a process known as ovulation. Most female mammals are “in heat,” or sexually receptive to males, only around the time of ovulation. This period of sexual receptivity is called estrus, and the reproductive cycle is therefore called an estrous cycle. The females continue to cyc...
mother’s uterine lining. Because the fetal and maternal blood vessels are in very close proximity in the placenta, the fetus can obtain nutrients by diffusion from the mother’s blood. The functioning of the placenta is discussed in more detail in chapter 60. Among mammals that are not seasonal breeders, the females un...
a total of four haploid spermatids are produced by each primary spermatocyte (figure 59.11). All of these cells constitute the germinal epithelium of the seminiferous tubules because they “germinate” the gametes. In addition to the germinal epithelium, the walls of the seminiferous tubules contain nongerminal cells kn...
es at around 34°C, slightly lower than the core body temperature (37°C). This lower temperature is required for normal sperm development in humans. Bladder Ureter Urethra Penis Seminal vesicle Ejaculatory duct Prostate gland Cowper's (bulbourethral) gland Vas deferens Epididymis Testis Scrotum FIGURE 59.10 Organization...
idymis, and they must remain there for at least 18 hours before their motility develops. From the epididymis, the sperm enter another long tube, the vas deferens, which passes into the abdominal cavity via the inguinal canal. The vas deferens from each testis joins with one of the ducts from a pair of glands called the...
fertilizing it are extraordinarily high, and the acrosomes of several sperm need to interact with the egg before a single sperm can penetrate the egg. Males with fewer than 20 million sperm per milliliter are generally considered sterile. Despite their large numbers, sperm constitute only about 1% of the volume of the...
negative feedback inhibition discussed in chapter 56 applies to the control of FSH and LH secretion (figure 59.15). The hypothalamic hormone, gonadotropinreleasing hormone (GnRH), stimulates the anterior pituitary gland to secrete both FSH and LH. FSH causes the Sertoli cells to release a peptide hormone called inhibi...
functional units of the ovary. At puberty, the granulosa cells begin to secrete the major female sex hormone estradiol (also called estrogen), triggering menarche, the onset of menstrual cycling. Estradiol also stimulates the formation of the female secondary sexual characteristics, including breast development and th...
and rabbits. Menstrual and Estrous Cycles At birth, a female’s ovaries contain some 2 million follicles, each with an ovum that has begun meiosis but which is arrested in prophase of the first meiotic division. At this stage, the ova are called primary oocytes. Some of these primary-oocyte-containing follicles are sti...
(haploid) Ovum (haploid) MEIOSIS I First polar body MEIOSIS II Second polar body FIGURE 59.19 The meiotic events of oogenesis in humans. A primary oocyte is diploid. At the completion of the first meiotic division, one division product is eliminated as a polar body, while the other, the secondary oocyte, is released d...
, so that by the time it enters the uterus, it is a hollow sphere of cells called a blastocyst. The blastocyst implants within the wall of the uterus, where it continues its development. (The egg and its subsequent stages have been enlarged for clarification.) 1208 Part XIV Regulating the Animal Body Luteal Phase After...
uteal phase, causing the built-up endometrium to be sloughed off with accompanying bleeding. This process is called menstruation, and the portion of the cycle in which it occurs is known as the menstrual phase of the endometrium. If the ovulated oocyte is fertilized, however, regression of the corpus luteum and subsequ...
fertilized. Chapter 59 Sex and Reproduction 1209 59.4 The physiology of human sexual intercourse is becoming better known. Physiology of Human Sexual Intercourse Few physical activities are more pleasurable to humans than sexual intercourse. The sex drive is one of the strongest drives directing human behavior, and as...
penis rub the clitoral hood against the clitoris. The nervous stimulation produced by the repeated movements of the penis within the vagina elicits a continuous response in the autonomic nervous system, greatly intensifying the physiological changes initiated during the excitement phase. In the female, pelvic thrusts ...
that is deeply ingrained in the female limits sexual receptivity to those periods of the sexual cycle when she is fertile. In humans and a few species of apes, the female can be sexually receptive throughout her reproductive cycle, and this extended receptivity to sexual intercourse serves a second important function—...
average 4 to 25% for diaphragms, perhaps because of the propensity to insert them carelessly when in a hurry. Failure rates for cervical caps are somewhat lower. Sperm Destruction A third general approach to birth control is to eliminate the sperm after ejaculation. This can be achieved in principle by washing out the...
from entering uterus Capsules surgically implanted under skin slowly release hormone that blocks ovulation Injectable contraceptive (medroxyprogesterone; Depo-Provera) Injection every 3 months of a hormone that is slowly released and prevents ovulation Probably similar to that of diaphragm 10–25.03 1 No dangerous side...
. Oral contraceptives provide a very effective means of birth control, with a failure rate of only 1 to 5%. In a variation of the oral contraceptive, hormone-containing capsules are implanted beneath the skin. These implanted capsules have failure rates below 1%. 1212 Part XIV Regulating the Animal Body Vas deferens wi...
ization A completely effective means of birth control is sterilization, the surgical removal of portions of the tubes that transport the gametes from the gonads (figure 59.23). Sterilization may be performed on either males or females, preventing sperm from entering the semen in males and preventing an ovulated oocyte ...
, where it implants if fertilized. • If fertilization does not occur, the corpus luteum regresses at the end of the cycle and the resulting fall in estradiol and progesterone secretion cause menstruation to occur in humans and apes. 3. Briefly describe the function of seminal vesicles, prostate gland, and bulbourethral...
development. Developmental Processes during Neurulation. The mesoderm of chordates forms a notochord, and the overlying ectoderm rolls to produce a neural tube. How Cells Communicate during Development. Cellto-cell contact plays a major role in selecting the paths along which cells develop. Embryonic Development and V...
the female reproductive tract during mating. The sperm swim up the reproductive tract until they encounter a mature egg or oocyte in an oviduct, where fertilization occurs. Fertilization consists of three stages: penetration, activation, and fusion. Penetration As described in chapter 59, the secondary oocyte is relea...
perm nucleus Acrosome Jelly coat Cortical granule secreting contents into perivitelline space Vitelline membrane Acrosomal process Egg plasma membrane Sperm nucleus Altered vitelline membrane prevents further sperm penetration (a) (b) FIGURE 60.3 Sperm penetration of a sea urchin egg. (a) The stages of penetration. (b)...
ization is the fusion of the entering sperm nucleus with the haploid egg nucleus to form the diploid nucleus of the zygote. This fusion is triggered by the activation of the egg. If a sperm nucleus is microinjected into an egg without activating the egg, the two nuclei will not fuse. The nature of the signals that are ...
.5 Yolk distribution in three kinds of eggs. (a) In the lancelet, a primitive chordate, the egg consists of a central nucleus surrounded by a small amount of yolk. (b) In a frog egg there is much more yolk, and the nucleus is displaced toward one pole. (c) Bird eggs are complexly organized, with the nucleus just under ...
the body. Chapter 60 Vertebrate Development 1219 Reptiles and Birds The eggs produced by reptiles, birds, and some fish are composed almost entirely of yolk, with a small amount of cytoplasm concentrated at one pole. Cleavage in these eggs occurs only in the tiny disc of polar cytoplasm, called the blastodisc, that li...
the developmental fate of each cell. This positional information is of particular importance in the orientation of mammalian embryos, setting up different patterns of development along three embryonic axes: anterior-posterior, dorsal-ventral, and proximaldistal. For a short period of time, just before they implant in ...
surface of the blastula in a carefully orchestrated activity called gastrulation. The events of gastrulation determine the basic developmental pattern of the vertebrate embryo. By the end of gastrulation, the cells of the embryo have rearranged into three primary germ layers: ectoderm, mesoderm, and endoderm. The cell...
chenteron, the future anus, is known as the blastopore. This process produces an embryo with two cell layers: an outer ectoderm and an inner endoderm. Soon afterward, a third cell layer, the mesoderm, forms between the ectoderm and endoderm. In lancelets, the mesoderm forms from pouches that pinch off the endoderm. The...
figure 60.11). Ectoderm Blastocoel Animal pole Ectoderm Blastocoel Archenteron Blastocoel Mesoderm Vegetal pole (a) Dorsal lip of blastopore Neural plate Neural plate (b) (c) Neural fold Ectoderm Mesoderm Endoderm Dorsal lip Yolk plug Ventral lip (d) (e) FIGURE 60.11 Frog gastrulation. (a) A layer of cells from the ani...
the invagination of the blastula, and the mesoderm layer forms from pouches pinched from the endoderm. In those vertebrates with extensive amounts of yolk, gastrulation requires the involution of surface cells into a blastopore or primitive streak, and the mesoderm is derived from some of these involuted cells. Blasto...
mal cells situated above the notochord invaginates, forming a long crease, the neural groove, down the long axis of the embryo. The edges of the neural groove then move toward each other and fuse, creating a long hollow cylinder, the neural tube (figure 60.14), which runs beneath the surface of the embryo’s back. The n...
of the vertebrates because neural crest cells, after migrating to different parts of the embryo, ultimately develop into the structures characteristic of (though not necessarily unique to) the vertebrate body. The differentiation of neural crest cells depends on their location. At the anterior end of the embryo, they ...
these muscles. A major blood vessel called the aortic arch passes through each of the embryonic bars. Lined by still more neural crest cells, these Neural crest Neural crest (d) Neural tube (e) bars, with their internal blood supply, become highly branched and form the gills of the adult. Because the stiff bars of the...
how these cell layers know where they are. For example, when cells of the ectoderm situated above the developing notochord give rise to the neural groove, how do these cells know they are above the notochord? The solution to this puzzle is one of the outstanding accomplishments of experimental embryology, the study of...
. This phenomenon as a whole is known as induction. The process of induction that Spemann discovered appears to be the basic mode of development in vertebrates. Inductions between the three primary tissue types—ectoderm, mesoderm, and endoderm—are referred to as primary inductions. Inductions between tissues that have ...
differentiation of that particular cell into a liver cell entail the physical loss of the information specifying other cell types? No, it does not—but cells progressively lose the capacity to express ever-larger portions of their genomes. Development is a process of progressive restriction of gene expression. Some cel...
development of a mammalian embryo, traces can be seen of appendages and organs that are apparently relicts of more primitive chordates. For example, at certain stages a human embryo possesses pharyngeal slits, which occur in all chordates and are homologous to the gill slits of fish. At later stages, a human embryo al...
law is not literally true when stated in this way because embryonic stages are not reflections of adult ancestors. Instead, the embryonic stages of a particular vertebrate often reflect the embryonic stages of that vertebrate’s ancestors. Thus, the pharyngeal slits of a mammalian embryo are not like the gill slits its...
. In mammals, the embryonic cells form an inner cell mass that will become the body of the embryo and a layer of surrounding cells called the trophoblast (see figure 60.9). The trophoblast implants into the endometrial lining of its mother’s uterus and becomes the chorionic membrane (figure 60.20). The part of the chor...
brate Development 1231 60.5 Human development is divided into trimesters. First Trimester The development of the human embryo shows its evolutionary origins. Without an evolutionary perspective, we would be unable to account for the fact that human development proceeds in much the same way as development in a bird. In ...
ization, the developing chorion forms branched extensions, the chorionic frondosum (fetal placenta) that protrude into the endometrium (figure 60.21). These extensions induce the surrounding endometrial tissue to undergo changes and become the decidua basalis (maternal placenta). Together, the chorionic frondosum and d...
. The tubular heart develops its four chambers and starts to pulsate rhythmically, as it will for the rest of the individual’s life. At 70 beats per minute, the heart is destined to beat more than 2.5 billion times during a lifetime of 70 years. Over 30 pairs of somites are visible by the end of the fourth week, and th...
What remains of development is essentially growth. At around 10 weeks, the secretion of human chorionic gonadotropin (hCG) by the placenta declines, and the corpus luteum regresses as a result. However, menstruation does not occur because the placenta itself secretes estradiol and progesterone (figure 60.24). In fact,...
the uterus without special medical intervention. The third trimester is predominantly a period of growth rather than development. The weight of the fetus doubles several times, but this increase in bulk is not the only kind of growth that occurs. Most of the major nerve tracts in the brain, as well as many new neurons...
the rate eventually increases to one contraction every two to three minutes. Finally, strong contractions, aided by the mother’s pushing, expel the fetus, which is now a newborn baby. Wall of uterus Vagina FIGURE 60.25 Position of the fetus just before birth. A developing fetus is a major addition to a woman’s anatomy...
ary alveoli to produce milk. Sensory impulses associated with the baby’s suckling trigger the posterior pituitary gland to release oxytocin. Oxytocin stimulates contraction of the smooth muscle surrounding the alveolar ducts, thus causing milk to be ejected by the breast. This pathway is known as the milk-ejection refl...
FIGURE 60.27 Allometric growth. In young chimpanzees, the jaw grows at a faster rate than the rest of the head. As a result, the adult chimpanzee head shape differs greatly from its head shape as a newborn. In humans, the difference in growth between the jaw and the rest of the head is much smaller, and the adult head...
• Early development • Preembryonic development • Cell differentation • Neurulation involves the formation of a structure found only in chordates, the notochord and dorsal hollow nerve cord. • The formation of the neural crest is the first developmental event unique to vertebrates. Most of the distinctive structures as...
niche Make an Outline Create an outline of this section. Use the headings to organize your outline. List details from what you have read to complete your outline. 1. List three ways ecologists study interactions between organisms. Reading Essentials Chapter 2 Principles of Ecology 11. 011-022 GHSB RESG-874600.indd 11 ...
amount of rainfall, the amount of sunlight, the type of soil, the range of air and soil temperatures, and the nutrients available in the soil. Organisms are adapted to the abiotic factors in their natural environment. If an organism moves to a different location with a different set of abiotic factors, the organism mu...
not be enough resources for all members of the population. The population will get smaller until it reaches a number that can be supported by the available resources. 6. Draw Conclusions What is a biological community? If a population is growing, what can you conclude about the amount of resources available to the org...
compete? Competition occurs when organisms need to use the same resource at the same time. Organisms compete for such resources as food, water, space, and light. When strong organisms compete with weak organisms, the strong organisms usually survive. During a drought, water might be scarce for many organisms. Strong o...
examples of predation that you have seen or of which you have learned. 9. Apply Clown ﬁ sh live among sea anemones. The anemones provide protection for the clown ﬁ sh. The clown ﬁ sh eats food missed by the sea anemones. What term best describes this relationship biologygmh.com Chapter 2 Principles of Ecology 15 011-0...
prey on other heterotrophs are known as carnivores (KAR nuh vorz). Wolves and lions are carnivores. Omnivores (AHM nih vorz) eat both plants and animals. Bears, humans, and mockingbirds are examples of omnivores. 16 Chapter 2 Principles of Ecology Reading Essentials. 011-022 GHSB RESG-874600.indd 16 011-022 GHSB RESG-...
hopper Snake Carnivore 2. Explain How do organisms in an ecosystem depend on detritivores? Picture This 3. Label Draw a circle around the autotroph. Draw a box around the heterotrophs Reading Essentials Chapter 2 Principles of Ecology 17 011-022 GHSB RESG-874600.indd 17 011-022 GHSB RESG-874600.indd 17 3/17/06 10:55:31...
Before You Read By looking at calendars, you can observe cycles, such as the cycle of the school year and summer vacation. On the lines below, write about cycles in your life. Read about the cycles in nature. Read to Learn Cycles in the Biosphere The law of the conservation of mass states that matter is not created or...
. Scientists use the name biogeochemical cycle to describe the combination of processes that exchange matter through the biosphere. How does water cycle? Evaporation occurs when liquid water changes into water vapor—a gas—and enters the atmosphere. Water evaporates from bodies of water, from water in the soil, and from...
shown in the ﬁ gure below. These bacteria live in water, the soil, or grow on the roots of some plants. Nitrogen ﬁ xation is the process of capturing and changing nitrogen into a form that plants can use. Humans add nitrogen to the soil when they apply chemical fertilizers to a lawn or to crops. Picture This 4. Determ...
B RESG-874600.indd 22 011-022 GHSB RESG-874600.indd 22 3/17/06 10:55:49 AM 3/17/06 10:55:49 AM 3 section ● 1 Communities, Biomes, and Ecosystems Community Ecology Before You Read On the lines below, list several plants and animals that live in your community. Then name one organism that would have trouble surviving whe...
.) a. abiotic b. biotic Picture This 3. Explain what the curved graph line represents. What factors limit populations in communities? Any abiotic factor or biotic factor that restricts the numbers, reproduction, or distribution of organisms is called a limiting factor. Abiotic limiting factors include sunlight, climate...
community in an area of bare rock that does not have topsoil. For example, suppose a lava ﬂ ow alters an ecosystem. The lava hardens to form bare rock. Usually, lichens begin to grow on the rock ﬁ rst. Because lichens and some mosses are among the ﬁ rst organisms to appear, they are called pioneer species. Pioneer spe...
grouped into biomes based on the plant communities within them. What You’ll Learn the three major climate zones the major abiotic factors how climate and biotic factors differ among land biomes Identify Biomes Highlight each term that introduces a biome. Then use a different color to highlight important facts about ea...
major land biome. What are the characteristics of tundra? Below the polar ice caps, a band of tundra runs across northern North America, Europe, and Asia, as shown in the ﬁ gure below. Tundra is a treeless biome with a layer of permanently frozen soil called permafrost beneath the surface. Mosses, lichens, and short g...
found on many continents. Grasslands are called steppes in Asia; prairies in North America; pampas, llanos, and cerrados in South America; savannahs and velds in Africa; and rangelands in Australia. The fertile soils of grasslands support a thick cover of grasses. Grazing animals and ﬁ res keep grasslands from becomin...
not ﬁ t the deﬁ nition of a biome because their climate and plant and animal life depend on elevation. Polar regions are also not true biomes because they are ice masses that lack land areas with soil. How do conditions change with elevation? If you climb a mountain, you might notice that temperatures fall as you clim...
Aquatic ecosystems include freshwater, transitional, and marine ecosystems. Freshwater Ecosystems Ponds, lakes, streams, rivers, and wetlands are freshwater ecosystems. The graph on the left below shows that only about 2.5 percent of Earth’s water is freshwater. The graph on the right shows that 68.9 percent of the fr...
�� ow. In slow-moving water, insect eggs are the main food source for many ﬁ sh. Calm water also provides a home for crabs, tadpoles, and frogs. Picture This 2. Label the area of the river where most sediment will be deposited. On the lines below, explain why. How does altitude affect life in lakes and ponds? Some lake...
aquatic ecosystems can be areas where land and water mingle. They can also be areas where salt water and freshwater mix. Examples of transitional aquatic ecosystems are wetlands and estuaries. What kinds of life thrive in wetlands? Wetlands are areas of land that are saturated with water and support aquatic plants. Ex...
zone is submerged. As tides and waves move out, the intertidal zone is exposed. Only a few species of algae and mollusks live where the highest tides reach. A diversity of species, including algae and small animals such as snails, crabs, sea stars, and ﬁ shes, live in areas that are submerged during high tide. The bot...
of bacteria, fungi, sponges, sea anemones, and ﬁ shes live in shallower parts of the benthic zone. The abyssal zone is the deepest region of the ocean. The water is very cold. Most organisms depend on pieces of food that drift down from the zones above. Hydrothermal vents on the seaﬂ oor release hot water, hydrogen su...
, and bacteria. All populations have certain characteristics, such as population density, spatial distribution, and growth rate. What are common patterns of dispersion? Population density is the number of organisms per unit area. For example, there was an average of four American bison per square kilometer in Northern ...
example, populations are limited by weather events such as drought, ﬂ oods, and hurricanes. Human activities can also be density-independent limiting factors. For example, dam building alters the water ﬂ ow of rivers, limiting some species. Pollution resulting from human activities reduces the available resources by m...
the wolf population increased. Follow the events in the ﬁ gure below to see how the populations of wolves and moose depend on one another. As the population density of one decreases, the population density of the other increases Picture This 4. Predict how the cycle might change for the moose population if the wolves ...
035-042 GHSB RESG-874600.indd 38 035-042 GHSB RESG-874600.indd 38 3/17/06 12:06:40 PM 3/17/06 12:06:40 PM Carrying Capacity The graph below shows logistic growth. Notice that the graph begins in a J-shaped pattern of exponential growth, as in the previous graph. Then limiting factors slow population growth, causing th...
2 GHSB RESG-874600.indd 39 3/17/06 12:06:43 PM 3/17/06 12:06:43 PM 4 section ● Population Ecology Human Population 2 Human population growth changes over time. What You’ll Learn the age structure of nongrowing, slowly growing, and rapidly growing countries consequences of continued population growth Before You Read Thi...
and a high standard of living. Early in its history, the United States had a high birthrate and a high death rate. Many children died before reaching adulthood. Typically, individuals died by their early forties. In recent years, the birthrate in the United States has decreased a lot. The average lifespan is now more ...
the largest portion of the population is in the pre-reproductive stage, as in Kenya, the population is growing rapidly. When the smallest portion is pre-reproductive, as in Germany, the population is decreasing. When the reproductive and pre-reproductive groups are roughly equal, as in the United States, the populatio...
. Other populations have little. A population with more genetic diversity is more likely to survive during environmental changes, an outbreak of disease, or the disappearance of a food source. Biodiversity maintains a healthy biosphere. What You’ll Learn the three types of diversity why biodiversity is important the di...
043-054 GHSB RESG-874600.indd 44 3/17/06 12:16:43 PM 3/17/06 12:16:43 PM Why might a species be valuable someday? One reason to preserve biodiversity is that wild species might someday be needed to create better crops for growing food. Biologists are beginning to learn how to transfer genes that control inherited char...
in ecosystems. What You’ll Learn factors that threaten biodiversity how the decline of one species can impact an ecosystem Before You Read You have probably read or heard about environmental issues in the news. On the lines below, list some environmental problems. Then read to learn about the possible consequences of ...
Extinctions Since 1600 Group Mainland Island Ocean Mammals Birds Reptiles Amphibians Fish Invertebrates Flowering plants 30 21 1 2 22 49 245 51 92 20 0 1 48 139 4 0 0 0 0 1 0 Picture This 2. Identify What two groups of living things have the highest rate of extinction? Estimated Number of Species Percent of Group Exti...
ocelots for their fur and white rhinoceroses for their horns. Why is habitat loss a problem? Overexploitation was once the main cause of extinction. Today, the main cause is the loss or destruction of habitat. When a habitat is destroyed, the native species might have to move or they will die. An example of habitat de...
harmed most by the edge effect. How does pollution impact biodiversity? Pollution damages ecosystems and decreases biodiversity by releasing harmful substances into the environment. Pesticides and industrial chemicals are examples of pollutants that are in food webs. Organisms ingest these substances in their food or ...
do nonnative species change ecosystems? Organisms that have been moved to a new habitat are known as introduced species. In their native habitat, these organisms are kept in balance by predators, parasites, and competition with other species. When they are introduced into a new area, these controlling factors are not ...
G-874600.indd 51 043-054 GHSB RESG-874600.indd 51 3/17/06 12:17:02 PM 3/17/06 12:17:02 PM ■ ■ ■ 2. Identify Which of these energy resources is a nonrenewable resource? (Circle your answer.) a. wind b. gasoline c. solar 3. Identify two ways people can sustainably use resources. What are examples of renewable resources? ...
00.indd 52 043-054 GHSB RESG-874600.indd 52 3/17/06 12:17:06 PM 3/17/06 12:17:06 PM How much of the world’s land is protected? Many countries have established their own natural parks and nature reserves. Today about 7 percent of the world’s land is protected for biodiversity. Biodiversity in these areas can be threaten...
d 53 043-054 GHSB RESG-874600.indd 53 3/17/06 12:17:08 PM 3/17/06 12:17:08 PM What kinds of ecosystems need to be restored? Natural causes, such as volcanic eruptions or ﬂ oods, can destroy biodiversity. People can destroy biodiversity when they do not use resources sustainably. Damaged ecosystems might take a long tim...
043-054 GHSB RESG-874600.indd 54 3/17/06 12:17:10 PM 3/17/06 12:17:10 PM 6 section ● Chemistry in Biology Atoms, Elements, and Compounds 1 Matter is composed of tiny particles called atoms. What You’ll Learn the particles that make up atoms the difference between covalent bonds and ionic bonds about van der Waals forc...
oxygen. How are isotopes identiﬁ ed? Atoms of the same element have the same number of protons and electrons but sometimes different numbers of neutrons. Atoms of the same element with different numbers of neutrons are called isotopes. Isotopes are identiﬁ ed by adding the number of protons and neutrons. Carbon-12 has...
17/06 1:06:06 PM Chemical Bonds The force that holds substances together is called a chemical bond. Chemical bonding involves electrons. Electrons travel around the nucleus of an atom in energy levels. Each energy level can hold only a certain number of electrons. The ﬁ rst energy level, which is closest to the nucleus...

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